Spray nozzle assemblies having a spray nozzle head which is secured to a nozzle body formed with a flow passageway that communicates with a discharge orifice end in the nozzle are known. For controlling the flow of an application fluid through the nozzle assembly, a selectively movable valve control needle is disposed within the flow passageway. To facilitate pressurized air atomization of the application fluid as it is discharged from the nozzle assembly, an air cap is typically disposed immediately downstream of the spray nozzle head so as to define an air chamber.
It is common to pneumatically operate the valve control needle of these spray nozzle assemblies in such a way to achieve a predetermined relatively high speed cyclic movement between open and closed positions in order to achieve the desired timing and a projected developed spray pattern. Many manufacturing and processing facilities utilize large numbers of these pneumatically operated spray nozzles. In order to operate all of the spray nozzles, such facilities require substantial pressurized control air capacity, which can be very costly.
One problem with such pneumatically controlled spray nozzle assemblies is that the valve needle must be sealed from the pressurized air which controls operation of the valve needle. This typically is done with a packing ring or seal. However, the packing ring or seal creates a significant drag on movement of the valve needle, limiting the rate at which the valve needle can cycle between the open and closed positions. One way in which to compensate for the friction loss caused by the packing rings or seals is to increase the pressure of the control air supply in the facility. Yet, this can be quite expensive. The packing rings or seals are also susceptible to excessive leakage due to poor fit or wear which, in turn, results in inefficient utilization of the pressurized control air supply at the facility. Another problem with the packing rings or seals is that they are difficult to assemble into the spray nozzle assembly.